1. Field of the Invention
The present invention relates to a technology for supporting endoscopic observation during surgery or examination using an endoscope inserted in a body cavity of a subject, and in particular to a technology for supporting endoscopic observation using a virtual endoscopic image representing the interior of a body cavity of a subject.
2. Description of the Related Art
In recent years, surgery using an endoscope, such as laparoscopic surgery and thoracoscopic surgery, is drawing attention. The endoscopic surgery is advantageous in that it does not require laparotomy, thoracotomy, or the like, and only needs to make two or three holes of few centimeters in diameter for insertion of an endoscope and a surgical tool, thereby significantly reducing the burden imposed on the patient. However, conducting surgery with a very limited field of view of the endoscope is highly difficult, and doctors require a lot of skill to conduct the endoscopic surgery. If a blood vessel or an organ of the patient is damaged by mistake and breeds during the endoscopic surgery, it is impossible to continue the endoscopic surgery and the doctor has to conduct conventional surgery involving laparotomy, thoracotomy, or the like.
On the other hand, a virtual endoscopy technology for generating a virtual endoscopic image, which is similar to an endoscopic image, from a 3D volume image taken with a CT device, or the like, is known. This technology is widely used in North America as a method for finding a tumor, in particular, a colorectal tumor, only by CT imaging without conducting endoscopic examination.
Further, a technology for supporting endoscopic surgery using a virtual endoscopic image has been proposed.
For example, Japanese Unexamined Patent Publication No. 2002-263053 (hereinafter, Patent Document 1) has disclosed a device that detects a position of an endoscope with a sensor, generates a virtual endoscopic image having an angle of view wider than that of the endoscope with setting the detected position of the endoscope as a view point, and displays the virtual endoscopic image and a real endoscopic image taken with the endoscope superimposed one on the other.
Further, Japanese Unexamined Patent Publication No. 2005-021353 (hereinafter, Patent Document 2) has disclosed a device that detects a real-time position of an endoscope to generate a virtual endoscopic image having the same field of view as that of the endoscope, where location of blood vessels in the field of view is visualized. The device also detects a real-time position of a surgical tool used during endoscopic surgery to generate a composite image in which an image representing the surgical tool is combined at the position of the surgical tool in the virtual endoscopic image, and displays the composite image and a real endoscopic image.
According to the techniques disclosed in these documents, however, although the virtual endoscopic image serves to compensate for the narrow field of view of the endoscope, the virtual endoscopic image has the same viewpoint as that of the real endoscopic image, i.e., is an image viewed from the same observation direction as that of the real endoscopic image. Therefore, depending on the positional relationship between the endoscope and a site of interest, such as a surgical tool or a site of surgical interest, the site of interest may not sometimes be shown in the virtual endoscopic image and the real endoscopic image, and the doctor cannot recognize the approach of the endoscope to the site of interest in such a case.